The present invention relates to a fixing unit for an electrophotographic copying machine wherein developing powder or toner disposed on the copy sheet in the pattern of an image is fused and caused to adhere to the copy sheet, representing after this operation the finished copy of the original. More particularly, the present invention relates to a fixing unit of the type in which the copy sheet is made to pass through the nip of a pair of rotating rollers having their surfaces suitably heated and normally called fusing rollers.